The present invention relates to a method of loading a liquefied gas from a first container into a second container without removal of vapor from the second container and to apparatus for use therewith.
The invention relates particularly to the filling of fuel storage tanks on vehicles propelled by engines adapted to operate on liquefied gaseous fuel. Such fuels include for example liquefied natural gas (L.N.G.), liquefied petroleum gas (L.P.G.) and liquefied hydrogen.
While it is accepted that the use of a gaseous fuel in an engine offers many attractive advantages, for example such fuels are clean, non-toxic, have a high calorific value and upon combustion yield a lower proportion of potential pollutants than conventional petroleum fuels, one disadvantage of these materials is their low density. To make available a convenient amount of gas in a limited spaced it is necessary to resort to either very high pressure storage or liquefaction. The most accepted method of storing and transporting bulk quantities of gaseous materials is in the liquefied form and it is in this form that such fuels will be most likely stored on vehicles.
Storage of liquefied gases is preferably carried out in double walled vacuum-type containers having the vacuum space between the two walls filled with a material that inhibits radiation such as perlite insulation. Although the insulation of such containers is very efficient there is still some leakage of heat to the contents with time and consequently some production of vapor. This effect is enlarged when the container is a storage tank supplying fuel to an engine wherein the tank surface area to volume ratio is high and wherein the level of the liquid contents gradually drops as fuel is used up and the vapor space above increases.
An added inconvenience is that when liquefied gas from a bulk storage container is loaded into such a container some vaporization takes place of the delivered material because some intermediary fittings are at ambient temperature or the delivered or stored material as a result of temperature differences between them.
When containers for liquefied gases are filled care has to be taken that vapor therefrom is not discharged into the atmosphere both from the point of view of safety and the fact that the vapor is a loss that the customer has paid for. Present methods necessitate the use of closed circuit systems of conduits having provision for the evacuation of vapor from the container to be filled prior to or during delivery of liquefied gas and for the removal of the vapor to separate containers, which may also be the vapor space within the bulk storage container from which the liquefied gas is being withdrawn.
The above methods have several drawbacks, in particular, vapor extraction or pressure balance must take place before a filling procedure, the return of vapor through the systems and into the bulk storage container tends to increase the temperature and therefore the pressure within the first container.
The present invention therefore provides a method of loading a liquefied gas from a first container into a second container without removal of vapor from the second container.